The art of automated mounting and filling valve bags generally involves sequentially lifting an individual bag from the top of a stack of bags with a bill which is first inserted into the valve located in one of the bag bottoms. After insertion of the bill, a gripping means grips the opened valve around the bill, whereupon the bill is retracted. As the gripper maintains the valve in an opened position, the gripper device moves the bag to a material filling spout and positions the valve on the spout for filling. Subsequently the gripper opens leaving the bag on the spout and moves to repeat the procedure with another bag.
When being moved from the stack to the filling spout, conventional valve bags so employed, often shift relative to the gripper, thereby causing the valve to become misaligned with the spout. This displacement is attributable to inertial forces generated upon swinging the bag from the stack to the spout. Due to the configuration of a conventional bag, the gripper secures only the upper bag bottom containing the valve. Thus upon removal from the stack, the lower bag bottom freely hangs from the gripper. During fast movements, the inertial forces of the freely hanging, lower bottom result in displacement of the upper bottom relative to the gripper and, therefore, misalignment.
One solution to overcome this problem, is to associate properly placed suction devices with the gripper. Such devices, if designed to overcome the inertial forces, secure the relative position of the gripper and the bag, thereby eliminating the displacement problem. However, suction devices overly complicate the structure of the gripper device. Furthermore, in use, suction devices present considerable maintenance problems due to the particle filled environment associated with a conventional filling apparatus.
Turning to the manufacture of valve bags, generally, caution is exercised during the crimping or folding processes. Conventional adhesives employed to glue the bottoms, in practice, are not fully cured during folding operations. Because folding apparatus generally employs opposed, cooperating rollers or belts for folding, the folds are located at some distance relative to the freshly glued bottoms. If folding occurs along a line where the glued portions are pressed by the rollers or belts, the uncured adhesive is squeezed out from its original line of application and the bag quality is correspondingly diminished. Therefore, such folds are produced along lines avoiding contact between the glued bottoms and the rollers.